1. Field of the Invention
The present invention relates to a network control apparatus, a wireless terminal and a communication control method used in a distributed wireless network system, which performs wireless communication, while a plurality of wireless terminals are relaying information signal to each other.
2. Related Art
In the distributed wireless network in which a plurality of wireless terminals communicate with each other, a method for efficiently downloading by means of downloading in group is disclosed (for example, see Japanese Laid-open publication No. 2002-132613 (pages 1 to 8, FIG. 1).
The wireless distributed wireless network has an advantage in that it is possible to temporarily construct a LAN (Local Area Network) at a certain range, without connecting to a backbone network. In a future wireless communication, it is anticipated that other kinds of communication besides sound signal such as motion pictures and data will be performed frequently, the quantity of transmitted signal by the wireless terminals at a spot area or at mobile environment will rapidly increase, and the transmission rate will also increase.
When the information signal quantity increases or the transmission rate increases, there may be the possibility that the whole information signal cannot be received accurately with only one wireless terminal. Particularly, when the wireless terminal is moving at a high speed as in a train or a bus, or in a place where the wireless environment is bad, this problem is serious. In order to handle this problem, the present applicant has proposed a method in which when a wireless terminal requests reception of information signal in a large quantity, the wireless terminal cooperates with other wireless terminals in the same distributed wireless network to receive the desired information signal, the reception requesting terminal coordinates the information signal received by the respective wireless terminals, and the coordinated information signal is distributed to the wireless terminal which has requested reception (see Japanese Patent Application No. 2002-127282).
However, this method has two problems described below.    1. One of the wireless terminals in the distributed wireless network collects the information signal received by the respective wireless terminals and coordinates the information signal as single information signal. However, the processing becomes a large load according to the capacity of the terminal which performs processing.    2. Since the function and capacity are different for each wireless terminal in the distributed wireless network, if the reception processing is allocated to each terminal under the same condition, the processing time of the terminal having small capacity affects other wireless terminals.
Moreover, if it is assumed that the distributed wireless network is constructed in trains or buses, it is expected that the access to the distributed wireless network by the wireless terminals is too frequent. In such a case, the system in which a plurality of terminals simply cooperate with each other would never be preferable.